求教，为什么脚本运行是总会提示 grep 命令没有参数

学着写了一下 shell 脚本，用来备份数据库， 运行正常
但是每次运行都会先提示 Usage: grep [OPTION]... PATTERN [FILE]，之后才是"MySQL backup Starting!"

脚本贴上
#!/bin/bash
# 数据库登录参数
user="root"
password="*******!"
host="127.0.0.1"
port="3306"
db_name="www"
# 备份文件存放地址
backup_path="/root/backups/mysql"
# 当天年月日
date=$(date +"%Y-%m-%d")
# 是否删除过期数据
expire_backup_delete="OFF"
expire_days=7
backup_time=$date
backup_dir=$backup_location
welcome_msg="MySQL backup Starting!"
# 判断 mysql 实例是否正常运行
mysql_ps=`ps -ef |grep mysql |wc -l`
mysql_listen=`netstat -an |grep LISTEN |grep $mysql_port|wc -l`
if [ [$mysql_ps == 0] -o [$mysql_listen == 0] ]; then
echo "ERROR:MySQL is not running! backup stop!"
exit
else
echo $welcome_msg
fi
# 数据库到 SQL 文件
mysqldump -u$user -p$password -h$host -P$port $db_name > $backup_path/$db_name-$date.sql
flag=`echo $?`
if [ $flag == "0" ];then
echo "database mysql_backup_$db_name success backup to $backup_dir/$db_name-$date.sql.gz"
else
echo "database mysql_backup_$db_name backup fail!"
fi
# 备份写入日志
echo "$backup_path/$db_name-$date" >> $backup_path/log.txt
# 删除过期数据
if [ "$expire_backup_delete" == "ON" -a "$backup_location" != "" ];then
`find $backup_location/ -type f -mtime +$expire_days | xargs rm -rf`
echo "Expired backup data delete complete!"
fi